Method of manufacture of pressure sensor having a laminated substrate

ABSTRACT

A pressure sensor sub-assembly (18) has a solid-state sensing element (22) mounted on a laminated ceramic substrate (20) and has the electrical signal contacts (22a) on the sensing element electrically connected to connector pins (24) on the substrate. A manufacturing process can fabricate a batch of sub-assemblies on a substrate structure that is sub-divided to form the separate sub-assemblies. The sensor sub-assemblies can be tested, and graded, before or after the sub-division step, and then each mounted in a housing.

This application is a divisional of application Ser. No. 07/825,620,filed on Jan. 24, 1992, now U.S. Pat. No. 5,285,690 the contents ofwhich are expressly incorporated.

Background

This invention relates to apparatus and manufacturing methods forpressure sensors that employ pressure-sensitive diaphragms. It relatesin particular to apparatus and assembly methods, including mechanicaland electrical features, for a discrete sensor sub-assembly having asolid-state sensing element that includes the sensing diaphragm. Thesub-assembly provides a minimal configuration for testing the electricalresponse of the diaphragm to pressure variations, before assembly withina housing.

Typical solid-state pressure sensing elements mount a thin silicondiaphragm above an open chamber. Pressure variations cause the diaphragmto deflect into and out of the chamber. The deflections cause changes inan electrical parameter, typically capacitance or resistance, that canbe measured and converted into pressure-responsive information.

The use of solid-state pressure sensing elements in hostile workenvironments typically requires a housing that surrounds and protectsthe sensing element from direct contact with the fluid being measured.One conventional housing has a metal base covered with a flexibleisolation diaphragm that separates the sensing diaphragm from the fluidbeing measured, and that deflects with the changing pressure of thefluid. A non-corrosive, inert fill fluid is within the housing, betweenthe isolation diaphragm and the sensing diaphragm, and transmits thepressure being measured to the sensing diaphragm. Electrical leadscarrying signals from the sensing element to external contacts of thepressure sensor pass through an hermetic seal to exit from the housing.This seal is typically achieved separately for each contact with aglass-to-metal bond through the metal base.

The sensing element conventionally is tested after assembly within thehousing. This-results in needless expense of materials and labor, if thetesting reveals a defect, for example, in the sensing element or theconnections to it.

It accordingly is an object of this invention to provide an improvedapparatus and manufacturing method for diaphragm pressure sensordevices, including a low cost testable format.

It is a further object of the invention to provide an improved methodand apparatus for the low-cost manufacture of a silicon-diaphragmpressure sensor having superior performance.

Another object of the invention is to provide pressure sensor apparatus,and a manufacturing method for the apparatus, that employ a solid-statesensing element and that operates with minimal spurious signal artifactsdue to mechanical disturbance, e.g., from distortion or other unwantedstress, of the sensing element.

Other objects of the invention will be apparent from the followingdescription.

SUMMARY OF THE INVENTION

A pressure sensor sub-assembly according to the invention has alaminated substrate to which a solid state sensing element is secured.The sensing element has a sensing diaphragm, and either side of thesensing element can be stimulated by a pressure that is to be testedrelative to the pressure on the other side. In a typical configuration,a pressure passage through the substrate communicates with a chamber onone side of the diaphragm of the sensing element.

The substrate preferably is a laminate of at least two layers ofceramic. Each ceramic layer is apertured to form holes for electricalconnections and for the pressure passage, and electrical conductors areformed in the holes to provide sealed electrical feed-throughconnections. The resultant layers are stacked and bonded together.Electrical connection pins, for external connection to the sensingelement, are attached to the substrate and connected with the conductorsformed in the holes.

The solid-state sensing element is mounted to the substrate by acompliant adhesive applied on the substrate with controlled thicknessand topography. Electrical connections are wired between contacts on thesensing element and, by way of the conductors in the holes in thesubstrate, the connection pins. A circuit element for measuring thediaphragm deflection by capacitive or resistive, e.g. piezo-resistive,techniques is typically provided on the sensing element.

At this stage of manufacture and with this structure, the sensorsub-assembly of the substrate and the sensing element is ready forfunctional testing. This includes testing the electrical response of thesensing element under different pressure conditions. The sensorsub-assembly can be sold as is, or used in various pressure sensingapplications.

In further accord with the invention, the foregoing fabrication sequenceand structure can be provided concurrently for a large number of sensorsub-assemblies by using, for each layer of the substrate, a sheet ofceramic sufficiently large to form one layer for the multiplesub-assemblies. The apertured ceramic sheets, with electrical conductorsfilling the holes, are stacked to form the laminated substrate. Onepreferred practice forms this laminated assemblage with green ceramicsheets. The laminate is scored to define each separate sensing element,and fired to form a monolithic structure. The connection pins areattached, the silicon sensing elements are mounted with the appliedadhesive, and the connections are wired to complete the concurrentassembly of the multiple sensor sub-assemblies.

The laminated substrate structure can be kept intact to this stage offabrication and for the testing of each sensor sub-assembly, and canthen be subdivided to separate the sensor sub-assemblies into individualunits.

Alternatively, the substrate structure can be subdivided into separatesensor sub-assemblies at an earlier stage, generally subsequent tofiring and illustratively after the adhesive mounting of the solid-statesensing elements to the substrate.

Each separated and tested sensor sub-assembly typically is assembledinto a housing, which conventionally has a metal base. The connectionpins carried on the substrate are accessible externally of the housingthrough the metal base, by way of apertures through the base, forconnecting the sensor sub-assembly to further electrical equipmentexternal to the housing. The sealant that mounts the sensor sub-assemblyforms a hermetic seal between the substrate and the housing base. Anisolation diaphragm typically closes the housing, after a fill fluid isintroduced, for coupling pressures external to the isolation diaphragmto the sensing element within the housing.

This structure and assembly procedure attains diaphragm-type pressuresensor sub-assemblies that can be tested before final assembly into ahousing. Further, the structure and procedure can be advantageously usedto manufacture an array of many sensor sub-assemblies elementsconcurrently. The invention thus enables pressure sensor sub-assembliesto be fabricated at low cost, and yet have high performance operation.The resultant pressure sensor sub-assemblies further are readily givenfinal assembly into pressure-tight housings, without the costly andfragile glass-to-metal seals of prior structures, to form completelyhoused sensors.

A further feature of the invention is that the mounting of thesolid-state sensing element to the ceramic substrate, by the compliantadhesive, both provides a hermetic seal and isolates the sensing elementsubstantially from mechanical disturbance, such as distortion or otherstress, of the substrate. This isolation of mechanical disturbanceminimizes erroneous signals from the sensing element.

Another advantage the invention provides for a pressure sensorsub-assembly is that both the solid-state sensing element and thesubstrate on which it is mounted can be of similar if not identicalmaterials and hence can have similar if not identical coefficients ofthermal expansion. In one example, each is of silicon. As a result,there is little if any differential thermal expansion/contractionbetween the substrate and the sensing element.

BRIEF DESCRIPTION OF DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be made to the following detailed description and theaccompanying drawings, in which:

FIG. 1 is a perspective view, partly cut away, of a pressure sensoraccording to one embodiment of the invention;

FIG. 2 is a perspective view of the sensor sub-assembly of the sensor ofFIG. 1;

FIGS. 3A and 3B show successive stages in the fabrication and testing ofthe sensor sub-assemblies of FIG. 2 in accordance with features of theinvention;

FIG. 4 is a perspective showing of the concurrent fabrication ofmultiple sensor sub-assemblies--illustrated in different stages offabrication--in accordance with FIGS. 2 and 3;

FIG. 5 is a perspective view, partly cut away, of another embodiment ofthe invention in which a sensor sub-assembly is inset into a ceramicsubstrate; and

FIG. 6 is a cross-sectional view of a sensor incorporating the sensorsub-assembly of FIG. 5.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS

A pressure sensor 10 according to the invention, as shown in FIG. 1, hasan outer housing 12 formed with a body 14. The body 14 is closed with anisolation diaphragm 16 and contains a pressure sensor sub-assembly 18.The illustrated sensor sub-assembly 18 has a ceramic substrate 20 onwhich is mounted a solid-state sensing element 22 that has a sensingdiaphragm 23. The sensor sub-assembly 18 has electrical connector pins24 projecting from the substrate 20 for external electrical connection.

The illustrated housing body 14 is apertured with a pressure passage 26that forms a fluid connection to the underside of the diaphragm 23. Thehousing body is also apertured with multiple apertures 30, parallel tocenter line 28, through which the connector pins 24 pass. The housingbody 14 has a lower bulkhead floor 14b and sidewalls 14c that form aninterior fill cavity 32 that is preferably centered on the axis of thepressure passage 26.

The sensor sub-assembly 18 is mounted with an adhesive sealant 34 to theflat interior surface of the bulkhead floor of the housing body. Theelectrical connector pins 24 project through that floor within theconnector apertures 30. The pins 24 are centered within the apertures 30to be isolated electrically from the walls of the apertures; insulatingsleeves over the pins or other means can also be provided to ensureelectrical isolation. The sensor sub-assembly 18 thus spans the pressurepassage 26 and the connector apertures 30 that extend through thebulkhead floor 14b. Further, the sealant 34 hermetically seals thesub-assembly 18 to the bulkhead floor.

FIG. 1 further shows that a sensor pressure passage 36 extends throughthe sensor substrate 20. This passage allows fluid communication betweenthe pressure passage 26 through the housing and a fluid chamber 38formed by solid state sensing element 22.

The side walls 14c of the housing body 14, in combination, form a fillcavity 32 above the housing floor 14b . The walls further define asealing rim to which the isolation diaphragm 16 is sealingly secured. Aninert pressure communicating fluid (not shown) fills the cavity 32 tocouple to the diaphragm 23 of the sensing element 22 external pressureexerted on the isolation diaphragm 16. The diaphragm 23 of the sensingelement 22 thus deflects according to the difference in pressure betweenthe pressure applied to the isolation diaphragm 16 and the pressure inthe chamber 38.

In the embodiment shown in FIG. 1, the sensor 10 may be used to measureeither differential pressure or gage pressure. In the case wheredifferential pressure is to be measured, a second pressure is applied tothe diaphragm 23 through the pressure passages 26 and 36. In one casewhere gage pressure is to be measured, the passages 26 and 36 are leftopen to the atmosphere. Finally, if the passages 26 and 36 are sealed oreliminated, the device can be used to measure absolute pressure appliedto the isolation diaphragm and coupled by the fill fluid to the top ofthe pressure sensing element 22.

FIG. 2, which is an enlarged view of the sensor sub-assembly 18, showsthat the illustrated sub-assembly 18 has the solid state sensing element22 mounted on an upper surface of the ceramic substrate 20. Electricalconductors 42 formed by metal-filled holes extend between the upper andlower surfaces of the substrate 20 and interconnect via conductive pads24a the connector pins 24, which project from the lower surface of thesubstrate 20, with conductive lands 44 formed on the substrate uppersurface. Conductive wires or metallic fingers 46 are bonded between thelands 44 and the contacts 22a on the upper surface of the solid statesensing element. With these electrical connections, the sensing element22 can be interconnected by way of the pins 24 to electronic dataacquisition instruments or other electrical equipment. A layer 48 ofbonding material, typically a compliant adhesive, bonds and seals thesensing element 22 to the substrate 20.

The pressure passage 36 extends through the layer 48 of bonding materialto communicate with the chamber 38 that the solid-state sensing element22 forms. With further reference to FIG. 2, the illustrated sensingelement 22 is an inverted box-like silicon structure with continuousperipheral walls, the edges of which are bonded to the substrate 20 byway of the adhesive bonding layer 48 for mechanical mounting andhermetic sealing. The central span of the sensing member, i.e., the baseof the box-like structure, is of reduced thickness to form thepressure-responsive diaphragm 23. The chamber 38 is thus defined by thebox-like structure and is sealed by way of the bonding adhesive layer 48from the pressure in the fill cavity 32 (FIG. 1).

The illustrated sensing element 22 has on the upper surface of thecentral portion, i.e., on the diaphragm 23 which it forms, electricalelements 22b that can be used to detect the pressure responsivedeflection of the diaphragm 23. The electrical elements 22b can be oneor more conductive films that form one or more capacitor plates or,alternatively, can be piezo-resistive. The electrical elements areconnected to the contacts 22a on the sensing element.

FIGS. 3A and 3B illustrate sequential steps of a process according tothe invention for fabricating the sensor sub-assembly 18 of FIGS. 1 and2 with a substrate 20 that is a laminate of three layers 52, 54 and 56.The first illustrated step 58a fabricates each substrate layer 52, 54and 56 from unfired, i.e., green, ceramic sheet material. Each layer ispunched to form apertures to form sensor pressure passage 36 and to formapertures 42a within which the electrical conductors 42 are subsequentlyformed.

In step 58b, the electrical connection apertures 42a are filled withconductive material, typically refractory metal ink, to form portions ofthe conductors 42. In a step 58c, the conductive lands 44 are formed, asby silk screening, on the upper surface of the upper layer 52. Also,conductive pads 24a for subsequent connection to the connector pins 24are formed, again preferably by silk screening, on the lower surface ofthe lower layer 56. The illustrated step 58c includes depositing anoptional conductive sealing pad 60 on the top surface of the upper layer52 as a continuous path peripherally outward of the lands 44. Thisoptional sealing pad 60 is engaged by a test fixture as described belowwith reference to the illustrated step 58j.

With further reference to FIG. 3A, a subsequent step 58d involvesstacking the green ceramic layers 52, 54 and 56, with the openings inregister with one another. The layers are then laminated together andfired under heat and pressure to form a single unitary structure and tobond the conductive ink segments into continuous electrical conductors42. Before the ceramic layers are bonded and fired in this manner, theillustrated fabrication of the ceramic substrate 20 includes forminggrooves or score lines 62 into the bottom and the top surfaces of thesubstrate. The grooves or score lines define the geometry of eachindividual discrete sensor sub-assembly into which the bonded sheetswill subsequently be separated.

In a subsequent step 58e, the electrical connector pins 24 are securedto the bottom surface of the substrate 20 by brazing them to theconductive pads 24a. The connecter pins are thus assembled to extendparallel to the axis 28, for functioning as male connecter pins formechanical and electrical engagement with corresponding female contacts.

FIG. 3B shows that in step 58f a compliant adhesive is deposited,preferably by stenciling, on the upper surface of each substrate 20 toform the bonding layer 48.

In the next fabrication step 58g, the solid-state sensing element 22 ispositioned on each substrate and pressed in place on the adhesivebonding layer 48. The adherent mounting bond, which the adhesive layer48 forms between the substrate 20 and the sensing element 22, is apressure-tight and hermetic seal. The adhesive bond is, however,sufficiently resiliently compliant to decouple the sensing element 22from stress in or deformation of the substrate 20. This stress isolationof the sensing element is important to avoid producing spurious signalsdue to unwanted distortion or stress of the diaphragm 23.

At this stage in the illustrated process, the batch of sensorsub-assemblies formed on the fired ceramic substrate is separated intodiscrete units, in step 58h. In a subsequent step 58i, the conductivewires 46 are bonded to the sensing element contacts 22a and to thesubstrate lands 44. The structural fabrication of each pressure sensorsub-assembly 18 is now complete.

In the illustrated next step 58j, each sensor sub-assembly 18 issubjected to functional testing of the electrical output signals itproduces in response to selected pressure conditions. In the testillustrated, the sensor sub-assembly 18 is seated on a lower testfixture 66. The test fixture 66 has a pressure aperture 66a in fluidcommunication with the sensor pressure passage 36 and which is connectedto a reference test pressure, which can be the ambient pressure. Thefixture 66 also has electrical receptacles 66b that connect with theconnector pins 24 on the sensor sub-assembly 18 and that are connectedto external test instrumentation.

As also shown in FIG. 3B in step 58j, an upper test fixture 68 engagesthe top of the ceramic substrate 20 of the sensor sub-assembly 18 withan 0-ring-like seal 68a at the conductive sealing pad 60. The upper testfixture 68 receives a sequence of selected temperature controlled testpressures by way of a passage 69, and applies it to the top of thesubstrate and to the upper, outer surface of the sensing element 22.

The two test fixtures 66 and 68 shown in step 58j can thus subject thediaphragm 23 of the pressure sensor sub-assembly 18 to selecteddifferential pressures and temperatures, and the electrical response ofthe sub-assembly is monitored by the test instrumentation connected byway of the test fixture contacts 66b. This testing of the pressuresensor sub-assembly 18 is performed prior to the costly further steps ofmounting it in the housing 12, as described above with reference toFIG. 1. A sensor sub-assembly 18 determined to be faulty or defective inthe testing of step 58j can be discarded or reworked. Further, thesensor sub-assemblies can be classified according to actual measuredperformance, e.g. sensitivity, and may be installed in differenthousings accordingly.

The further assembly of a successfully tested sensor sub-assembly 18into the housing 12 of FIG. 1 proceeds with the steps of applying thesealant 34 to the housing base 14, and mountingly bonding the sensorsub-assembly 18 onto the sealant, with the sensor pressure passage 36 incommunication with the housing pressure passage 26 and with theconnection pins 24 freely passing through the connector apertures 30.

The interior cavity 32 of the structure is then filled with theincompressible fill liquid, and the isolation diaphragm 16 is secured inplace. This completes the fabrication of the sensor 10.

The sequence of certain steps in the foregoing fabrication process canbe changed, as will be understood by those skilled in the art offabricating hermetic packages for electrical semiconductor integratedcircuits with green ceramic sheets. For example, the separation of themultiple sensor sub-assemblies into separate devices, illustrated atstep 58h, can be performed at different points in the assembly process.As further examples, the bonding wires 46 can be installed and/or thefunctional testing can be performed before the separation step.

FIG. 4 summarizes selected steps of the foregoing fabrication of FIGS.3A and 3B by showing different successive stages in the concurrentfabrication of multiple sensor sub-assemblies 18 on a single stack oflaminated ceramic sheets. The illustration in FIG. 4, with differentsensor sub-assemblies 18 in different stages of fabrication, ishypothetical; in a typical actual practice all the sensor sub-assemblies18 being fabricated on a single substrate structure are processed alikeand hence are all at the same stage of fabrication at any given time. Inparticular, the substrate sections 20-1 and 20-2 of FIG. 4 havecompleted fabrication step 58e of FIG. 3A, and accordingly, eachsubstrate is laminated and has the connection pins 24 mounted thereon.

Substrate sections 20-4, 20-5 and 20-6 illustrate a fabrication in whichthe adhesive layer 48 is applied by a silk screen or stencil operation,in accord with step 58f. In both this instance and in the instance ofsubstrate section 20-3, the adhesive layer is confined to a selectedconfiguration encircling the opening of the sensor pressure passage 36.This, however, is generally not necessary because a small appliedpressure will re-open the pressure passage 36 by removing any film ofadhesive that might cover it after application by silk screen orstencil.

An alternative application of the adhesive layer 48 is illustrated onthe substrate section 20-3, which has a layer 48 of adhesive dispensedon it in the desired configuration to keep the passage 36 open.

The substrate sections 20-7 and 20-8 show the fabrication at thecompletion of step 58h, with the solid-state sensing element 22 bondedin place, by way of the adhesive layer 48, to the substrate structure.The further substrate sections 20-9 and 20-10 in FIG. 4 show theassembly upon completion of step 58i, with the conductive wires, 46bonded between the conductive lands 44 on the substrate sections and theelectrical contacts 22a of the sensing elements.

FIG. 4 also shows the grooves 62 that are scored into the ceramicsubstrate structure, preferably after lamination and before firing, tofacilitate the subsequent separation of the separate sensorsub-assemblies 20.

FIG. 5 shows another pressure sensor sub-assembly 70 according to theinvention that has a multiple-layer tiered substrate 72 that forms afloor and elevated side walls that form a recessed well 102. Asolid-state sensing element 74 is secured on the floor and seated withinthe recessed well.

The illustrated substrate 72 has five ceramic layers, namely threelayers 76, 78 and 80 of essentially identical rectangular shape and thecentral portions of which form the floor on which the sensing element 74is mounted; and two upper layers 82 and 84. The upper substrate layers82 and 84 have the same outer dimensions as the lower substrate layers,and each has a central rectangular opening. Each upper layer thusextends peripherally about the mounted sensing element 74 and forms thetiered walls of the recessed well. The central opening illustrated inthe uppermost substrate layer 84 is larger than the opening in the upperlayer at 82, to form an outwardly stepped or tiered recessed well.

As further shown in FIG. 5, the ceramic substrate 72 has electricalconductors 86 extending between the substrate bottom surface, i.e., thebottom surface of the lower layer 76, and the upper surface of the firsttiered layer 82. These electrical conductors 86 extend within holesthrough the substrate layers 76, 78, 80 and 82. As further illustratedby way of example, each illustrated conductor 86 follows two non-alignedpaths 86a and 86b through the substrate. The path 86b is offsetlaterally outwardly from the path 86a, relative to the central recessedwell 102. A laterally extending conductor path 86c electricallyinterconnects the two offset segments of each conductor. Thisarrangement of the conductors, on different paths through the substrate,enables the upper and lower connections to the substrate to be locatedindependently of one another.

Conductive lands 92 are plated on the lower surface of the substrate 72and in contact with the conductors 86. An externally accessible maleconnector pin 94 is mounted to the substrate 72 in electrical contactwith each land 92, suitably by brazing. Further conductive lands 96 areplated on the upper surface of the substrate layer 82, each inelectrical contact with the upper end of a conductor 86 and openlyaccessible on the exposed step-like upper surface of that substratelayer. Electrical wires 98 are bonded between the lands 96 and contacts74a on the sensing element 74, for electrically connecting apiezo-resistive or capacitive circuit element (not shown) on the sensingelement 74 with the connector pins 94.

The solid-state sensing element 74 can be identical to the one describedwith reference to FIGS. 1 through 4 and bonded to the platform of thesubstrate 72 by way of a layer 100 of compliant mounting adhesive. Achamber 105 defined between the central recess of the sensing element 74and the substrate floor is in fluid communication with a pressurepassage 104 through the substrate layers 76, 78 and 80, typically alongthe center-line 88 as shown.

The pressure sensor sub-assembly 70 of FIG. 5 is preferably fabricatedin a manner similar to that described above with reference to FIGS. 3Aand 3B for the sensor sub-assembly 18 of FIG. 2.

In particular, multiple sensor sub-assemblies 70 are fabricatedconcurrently, as shown in FIG. 5, by punching five green ceramic sheetsto form the multiple substrate layers 76, 78, 80, 82 and 84,respectively. The holes in each of the sheets which are to form theelectrical conductors 86 are filled with a conductive ink. Theconductive material for forming the interconnection conductor paths 86c,and for forming the lands 92 and 96, are plated on the correspondingsurfaces of the ceramic sheets. An optional further conductive sealingland 106 can be plated on the sheet that forms the upper substrate layer84.

The green ceramic sheets are then stacked, laminated and scored withscore lines 108, prior to firing. The firing operation bonds thesubstrate layers into a single unitary structure and electricallyinterconnects the conductor segments of each layer to form continuouselectrical conductors 86 between the upper lands 96 and the lower lands92. The fabrication continues with the mounting of the conductor pins94.

A subsequent fabrication step is the deposition of the bonding layer 100on the upper surface of the substrate layer 80.

The solid-state sensing elements 74 are then positioned and bonded inplace on the substrate, after which the wires 98 are bonded between theconductive lands 96 of the substrates and the contacts 74a of thesensing elements.

At this point in the fabrication, each pressure sensor sub-assembly 70is ready for functional testing. The arrayed multiple sensorsub-assemblies can be separated from one another either prior orsubsequent to the testing. The sensor sub-assemblies are separated alongthe score lines 108. The functional testing of each sensor sub-assembly70 can be performed in a manner similar to that described above withreference to step 58j in FIG. 3B.

A sensor sub-assembly 70 that meets the functional test criteria is, asshown in FIG. 6, mounted in a sensor housing 112 to form a pressuresensor 111. The illustrated housing 112 has a body 114, typically ofstainless steel or like material, that has a central recess. Theillustrated housing body forms a housing bulkhead floor 114a on whichthe sensor sub-assembly 70 is mounted by way of an adhesive bond 115that hermetically seals the lower surface of the sensor substrate 72 tothe recessed top of the bulkhead floor 114a. Connector passages 116extend through the housing bulkhead floor 114a and the sensorsub-assembly connector pins 94 extend within these openings. A pressurepassage 118 through the housing floor communicates with the passage 104and hence with the chamber 105 on one side of the diaphragm of thesensing element 74. An isolation diaphragm 122 is sealingly attached toa rim at the top of the housing body 114 and encloses a fill liquid 124that fills the cavity that is within the housing 112 and outward of thesensor sub-assembly 70.

In one practice of the invention as described above with reference tothe sensor 10 of FIG. 1 and a sensor 111 as shown in FIG. 6, thesubstrate is formed of the same green ceramic material used insemiconductor integrated circuit manufacturing, an example of which isavailable from Coors Electronics Package Company, Chattanooga, Tenn. andis designated 92% alumina ceramic, type 1 per ASTM D-24421. Thesolid-state sensing elements 22 and 74 for each sensor can be a siliconsensor chip as incorporated in the Series 840 Pressure Transmittermarketed by The Foxboro Company, U.S.A.; and as described in thecommonly-assigned application for U.S. patent Ser. No. 676,914 filed 28Mar. 1991 by C. Fung et al. The bonding adhesive for the layer 48 in theembodiment of FIGS. 1 and 2 and for the layer 100 in the embodiment ofFIGS. 5 and 6 can be a room temperature vulcanizing rubber adhesive ofthe type sold by The General Electric Company under the designationfluorosilicone rubber no. FSL7210.

Further, the bonding adhesive for the layer 34 of FIG. 1 and for thelayer 115 of FIG. 6, securing each sensor sub-assembly 18 and 70 to ahousing body 14 and 114, respectively, can be of the type soldcommercially by Ablestik Laboratories in Rancho Dominquez, Calif. underthe designation Ablefilm 550--2--004.

Other specific materials and fabrication processes for the structure andfor the fabrication of sensor sub-assemblies and complete sensors asdescribed above can employ conventional practices.

It will thus be seen that the invention efficiently attains the objectsset forth above. These include providing, at relatively low cost,pressure sensor apparatus and fabrication techniques for attaining adiscrete, functional and testable sensor subassembly, having a laminatedsubstrate, that can be assembled within a housing. The apparatus andmethod of the invention further provides high performance and ruggedpressure sensor apparatus, and with efficiencies in manufacturing stepsand in structural elements.

It will be understood that changes within known practices and materialsmay be made in the above constructions and in the foregoing steps andsequences of fabrication without departing from the scope of theinvention. It is accordingly intended that all matter contained in theabove description and shown in the accompanying drawings be interpretedas illustrative, and not in a limiting sense.

What is claimed as new and secured by Letters Patent is:
 1. In themanufacture of pressure sensor apparatus, the steps ofA. providing asubstrate having first and second opposed sides, said substrate beinglaminated of at least first and second layers and having electricalconductors extending between said opposed sides in apertures throughsaid substrate, said apertures being hermetically sealed, B. applying abonding layer on said first side of said substrate, C. securing to saidsubstrate electrical connector elements extending from said second sideof said substrate, said connector elements being disposed for removableand replaceable connection with mating connector elements, and D.bonding to said first side of said substrate, by said bonding layer, asensing element having a sensor diaphragm and electrical contacts, saidsensing element developing at said electrical contacts an electricalsignal in response to diaphragm deflection, and having said contactsconnected electrically to said conductors.
 2. In the manufacture ofpressure sensor apparatus according to claim 1, the further steps oflaminating said substrate of plural ceramic layers and providing saidsensing element of silicon.
 3. In the manufacture of pressure sensorapparatus according to claim 1, the further steps ofA. laminating saidsubstrate of plural ceramic layers and fabricating each said substratelayer for a plurality of sensor sub-assemblies concurrently from a sheetof unfired ceramic material by(i) forming apertures through said sheetand forming segments of said electrical conductors in said apertures,and (ii) laminating said sheets together and connecting respective onesof said conductor segments, for forming an arrayed plurality of saidsubstrates concurrently, each with said electrical conductors extendingtherein, and B. separating said arrayed substrates into separate onesfor each of the sensor sub-assemblies.
 4. In the manufacture of pressuresensor apparatus according to claim 3, the further steps ofA. stackingsaid sheets together and scoring said stacked layers for definingindividual ones of said sensor sub-assemblies, and subsequently firingsaid stacked and scored sheets of unfired ceramic material, thereby forlaminating said sheets together and for connecting respective conductorsegments together.
 5. In the manufacture of pressure sensor apparatusaccording to claim 1, the further steps ofA. defining with said sensingelement and said substrate a chamber between one side of the saidsensing element and said substrate and wherein said sensor diaphragm ofsaid sensing element deflects in response to the pressure differencebetween said chamber and the pressure on the other side of said sensingelement, and B. providing a pressure passage through said substratecommunicating with said chamber, and C. said step of applying saidbonding layer includes maintaining said pressure passage substantiallyunobstructed by the material of said bonding layer.
 6. In themanufacture of pressure sensor apparatus, the sequential steps ofA.providing a ceramic substrate having first and second opposed sides,said substrate being laminated of at least first and second layers andbeing apertured between said first and second sides with a throughpressure passage, said substrate further having electrical conductorsextending between said opposed sides, said substrate beingpressure-tight between said opposed sides except at said pressurepassage, B. applying a bonding layer on said first side of saidsubstrate, C. securing to said substrate electrical connector elementsextending from said second side of said substrate, said connectorelements being disposed for removable and replaceable connection withmating connector elements, D. bonding to said first side of saidsubstrate by said bonding layer, a solid-state sensing element having asensor diaphragm and electrical contacts, said sensing elementdeveloping at said electrical contacts an electrical signal in responseto diaphragm deflection, and further having said contacts connectedelectrically to said conductors, E. testing the electrical response ofsaid sensing element to pressure differentials between said first sideand said pressure passage at the connector elements, and F. assemblingsaid substrate, with said sensing element and said connector elements,within a housing.